For the preparation of metallic electrodes on a ceramic insulator, a PVD deposition method (physical vapour deposition) is currently used. The deposition of the electrode material takes place by spraying the target in an inert or reactive atmosphere and subsequent condensing of the forming layer on the insulator's surface. Due to its high sensitivity to deposition parameters, the PVD method has a relatively high scrap rate in industrial conditions. As deposition of layers cannot be localised precisely, the deposited layer is deposited on the entire tip of the insulator. Thus grinding must follow the deposition, during which the conductive layer is removed from undesirable areas, which makes the entire production process even more expensive. Moreover, such deposited layers show limited adhesion to ceramic insulators and thus decreased spark plug service life.
Electrode deposition using a laser combines several advantages. The additional material is applied in the form of a wire to a precisely localised place on the insulator. This operation is final and therefore no further grinding or cleaning operation on the insulator has to follow the weld deposition. Another advantage of this method is the possibility of very quick exchange of the weld deposition material and the insulator shape. The additional material is melted during weld depositing. Upon contact of the molten metal with the ceramics, its capillary action into the porous structure of the ceramics and very good mechanical anchoring of the layer takes place. This significantly improves the adhesion of the deposited layers against the layers prepared using the PVD method, thus also improving the service life of the spark plug. The use of the weld deposit material in the form of a wire leads to the elimination of losses of often very expensive materials (on the basis of Pt, W, Ir, etc.).
The goal of the presented invention is to increase the service life of spark plugs with an electrode deposited on the insulator by creating a diffusion interface between the insulator and the electrode, to decrease the scrap rate of the spark plugs and the time demands and price of the deposition process.